Tone frequency noise filter



June 24, 1969 BRANCH ET AL 3,451,502

TONE FREQUENCY NOISE FILTER Filed April 5, 1968 m/vew rofis JACK PBRANCH NOEL 0. DURHAM United States Patent 3,451,502 TONE FREQUENCYNOISE FILTER Jack P. Branch, 2627 Sherwood Ave., Charlotte, NC. 28207,and Noel 0. Durham, Charlotte, N.C.; said Durham assignor to said BranchFiled Apr. 3, 1968, Ser. No. 718,542 Int. Cl. H04r 25/02 US. Cl. 181-2320 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a process andmeans for improvement of speech understanding for an individual whosephysical surroundings cause a lack of ability to facilely discriminatebetween auditory speech pulsations and background noises. The presentinvention discloses means, including a resonant capsule member whichcapsule encases a vibratory member and a diaphragm, this capsule beingadapt-able for insertion within the outer portion of the auditory canal.The capsule and the members associated therewith, including inner andouter casings, filter extraneous background noise and transmit, on apreferential basis, those frequencies and vibrations which are essentialto perceptive discrimination of human speech. The capsule hasincorporated therein a vibratory element or elements having apre-selected peak frequency response or frequency discriminatoryproperties, and further includes means to shift the peak of thisresponse, and to broaden this response as to its frequency width.

Background of the invention Increasingly, modern industrial plants andmodern socalled street noises cause inabilities, on the part of thenormal auditory mechanism of an average human being, to discriminateadequately between those sound pulsations which represent intelligiblehuman speech and those background noises which are produced byextraneous, non-desirable sound generators, such as industrial machines,propelled vehicles, ventilating systems, etc.

As is explained in more detail hereinafter, to compensate for this lackof discrimination and decibel rise of overall sound, the auditory nervesof a normal human being involuntarily attempt to raise the threshold ofaudibility to a level directly correlated with the level of the increaseof the overall sound intensity to which the ear is subjected. Thus, forexample, as the background noise increases in intensity, there isgenerally a logarithmic increase in the threshold which the auditorynerve attempts to perceive. This natural phenomenon is selfdefeating, inthe sense that, as the auditory system raises its threshold, itsimultaneously loses, in substantially direct proportion to the raisingof the threshold, the ability to distinguish between desirable sounds,such as those contained in human speech, and those undesirablebackground noises whose intensity have caused the initial rise of thethreshold.

It thus becomes more and more difficult to communicate intelligibly, asthe background noise level is increased, whether measured in decibels orin dyne force. While a rise in the intensity of the human voice willbetter enable the person hearing the voice to maintain communication,this process is not satisfactory, since there is a reasonable level towhich the human voice can be raised and still be intelligible.

The tone frequency noise filter of the present invention is intended to,and does, suppress these undesirable background noises, which noises areapplied, along with speech intelligence, against the ear structure inthe form of auditory, oscillatory air signals. At the same time thefilter reinforces those frequencies which are necessary for articulateintelligible communication, The present invention thus lowers thethreshold of knowledge audibility, decreasing the voice intensity neededto supply intelligible audible signals to a bearer.

The prior art has described systems designed to decrease the amount ofsensations received by the normal auditory system. These prior artdevices are generally of one of two forms. In the first form, a simplestopper is utilized to lower the input to the auditory system. Obviouslysuch systems do not transmit intelligble sounds to the human brain. Thesecond form of these systems has generically included means to transmitvia simple amplification, some selected portion or portions of thosefrequencies which most commonly occur in human speech. Such prior artsystems have not solved the problem herein described, because they donot provide sufficient amplification and/ or selectability as to thatportion of the auditory spectrum whose transmission is desirable.Furthermore, such prior art systems do not selectively and effectivelysuppress the undesirable background noises.

In order to more adequately understand the problem involved, a briefdescription will herein be given of the functioning of the human voiceand its relation by atmospheric or air coupling to the human ear.

The main function of human speech is, obviously, to act as a source ofspeech energy, which is modified or modulated by the articulatory humansystem. This speech source provides human articulatory vibration of acomplex nature, both as to intensity and frequency, which in turnvibrates the atmosphere or air into which the speech is emitted. Theintensity and harmonics are modulated by this human system, as thesituation dictates to the speaker.

Essentially, intelligible reception of human speech must include theability to distinguish between sounds which are generically designatedas consonants. These consonants are emi'ted by the normal human being ata low frequency rate, generally centering in the vicinity of 325 cyclesper second and, in most instances, having their major energy contentincluded in a spectrum from 300 to 400 cycles.

It is to be understood, however, that due to possible changes in thearticulatory system, consonant sounds may be emitted in human speech inextreme ranges of from about 40 to about 3900 cycles.

In addition, and in order to provide intelligible communication, thehuman voice emits a series of vowels which are inter-connected in spacedtime relation to the consonant sounds and are relied upon by the humanbrain to provide intelligent perception, These vowel sounds, whilemelliferous as to sensory perception, in actuality constitute only aseries of high intensity pulses of spaced energy. The energy pulses"which are provided by the vowels, while adding to and augmenting thepleasurable sense of hearing, are not essential, except insofar as theyprovide a gap means between the spaced consonants.

Therefore, it is apparent, and is. known, that human intelligibleperception is based predominantly upon the sustained oscillations causedby the production of consonants by the human voice. Accordingly, as isalso known, any means which concentrates, in its application to thehuman auditory system. those frequencies in which the consonants arecentered, provides intelligible information to the human brain, so as toenable the brain to readily perceive intelligence contained in theauditory oscillations.

Due, by happenstance, to the selection of 60 c.p.s. for the operation ofmost electrically powered equipment and further due to the happenstancethat most so-called street noises occur generally in a range above 4,000c.p.s.

3 there is available to the human ear a range of frequencies in whichthe ear can distinguish intelligible speech, but in which range thebackground noises have relatively low intensity in comparison to theintensity of the human voice.

It is therefore the principal object of the invention to selectivelycouple to the human ear only those sounds which fall within this rangeof desirable human speech, while at the same time suppressing thetransmission to the human auditory system of those noises whosefrequencies do not fall within this range, so far as their major powercomponents are concerned.

The system of the present invention, therefore, serves to eliminateundesirable background noises, and facilitates auditory reception andbrain response to signals derived from the human voice. The intensity ofthese desirable signals, while low in decibel level relative to theoverall decibel strength including the background noises, is stronger inthe desired frequency of the speech spectrum.

The figures of the drawings FIGURE 1 is a schematic view of the humanear, many of the parts thereof being eliminated for simplification, withthe generic device of the invention inserted within the auditory canalleading from the outer ear to the interior portions of the auditorysystem.

FIGURE 2 is a front elevation of the invention.

FIGURE 3 is a view in cross section taken on the line 3-3 of FIGURE 2.

FIGURE 4 is a partial cross-sectional view of a different form of thetransmitting member of the invention.

FIGURE 5 is a similar view of another form of the transmitting member ofthe invention, while;

FIGURE 6 is a view of a third embodiment thereof.

Detailed description of the invention As shown in FIGURE 1, the humanauditory apparatus includes, among its essential components, an outerear designated as 10. This portion of the ear operates predominantly asa means for concentrating and funneling sound oscillations to theinterior elements of the auditory system 20. In effect, the outerportion of the ear consists of a horn which concentrates and transmitssound vibrations into nerve responses in the human brain, after thesesignals have traversed the other members of the auditory system, whoseessential components will now be described.

It is to be understood that the shape of this outer portion of the earserves to direct the vibrating column of air at maximum intensity intothe entrance of the auditory canal, this canal being designated in itsentirety as 11. This canal 11 in turn concentrates and feeds these airvibrations to a tympanic membrane 12, which in turn feeds the vibrationsto an ossicle chain 13 and to a fenestra 16. Thereafter, thosevibrations which are received by the fenestra are transformed by otherportions of the auditory system into nerve impulses, which aretransmitted to the brain, in order to convey thereto informationcontained in the pulses received by the ear. The inner end of theauditory canal is designated herein as 15.

The apparatus of the present invention is intended to be placed withinthe canal member .11 so as to effect speech discrimination relative tonoise background. This is accomplished by rejecting undesirable tonesand by transforming the voice portion of the received auditory energy ina manner such as to boost, preferably in time delaying fashion, speechenergy. For this purpose there is provided a frequency selectivevibrating member 50, contained within a capsule, designated in itsentirety as 40, positioned within the canal 11. Since the membranemember 12 and the ossicle chain 13 are normally substantially intact andare operatively coupled in the normal human auditory system, it is to benoted that they would, in the absence of the device of the presentinvention, be responsive to a wide frequency of sounds, including all ofthe undesirable background sounds.

Reference will now be made to a preferred detailed 4 embodiment of theinvention, as shown in more particular detail in FIGURES 2 and 3.

The capsule 40 preferably includes a base member having an inner casing42 and an outer casing 41. Positioned exteriorly, i.e., towards theanterior of the canal 11, when the capsule 40 is inserted within thecanal 11, is a sound transmission passage 44 to direct auditory airoscillations to vibrator 50 of diaphragm 53 which may be of any desiredconfiguration, but which, as herein shown in FIGURE 3, is defined by theare 45 of the casing 42 and a generally chordlike line designated as 46.Thus, in effect, auditory signals received by vibration of theatmosphere, and applied to the outer ear 10, are compressed into andpassed through the passage 44.

In normal usage of the apparatus of the invention it is intended that nofurther air column signals be transmitted through the ear canal otherthan those which enter the passage 44.

Those compressed sound waves which enter the passage 44 are in turndirected to a vibratory element, or vibrator, 50 and vibrate this memberthrough their contained energy pulses. This vibratory member 50 isoperatively associated with and, preferably, supported by .a diaphragmmember designated as 53. Positioned between the outer end wall 43 ofcasing 42 and the vibratory member '50 is an air resonating chamber 60capable of vibration, this chamber being hereinafter designated as aresonator, the rear wall surface of which is formed by said membrane 53.Connected to the one end of the resonating chamber 60 is an end wall 43having, for ease of insertion and removal, a projecting member orhandle, designated as 43' mechanically coupled thereto. This member is,in effect, a manually graspable projection.

From the above described elements it will be understood that, in normalassembly of the device thus far described, the chamber 60 is assembledby inserting therewithin the diaphragm 53 and its coupled vibrator 50within a generally annular member 46. Thereafter, end wall 43 isinserted within this member to complete the chamber 60. It is to beunderstood that this entire association or elements is incorporatedwithin inner casing 42.

v The vibratory member has a natural resonant frequency which ispreselected. This frequency preferably centers about 325 cycles persecond. Generally speaking, it is desired that that this resonantfrequency is within the range of a spectrum of from about 300 to about400 cycles per second. In extreme cases the resonant frequency mayinclude the ranges of from about 40 to about 3900 cycles per second.

The entire apparatus as described hereinabove and as describedhereinafter, further incorporates, as noted above, an outer shieldmember or casing 41 which serves to accomplish physical contact betweenthe capsule and the interior surfaces 14 of the ear canal.

To aid in insertion or removal from outer casing 41 and to aid ininsuring proper positioning of the inner casing 42, this latter memberpreferably has a projecting annular rib surface 47 which axiallyslidably co-acts with a groove 48 formed in the interior wall 49 of theouter casing element 41, which rib 47, upon insertion of the innercasing within the outer casing, is engaged by the groove. This couplingmay be achieved by means such as flexure, or bayonet coaction, or anysimilar means known in the art.

Referring again to the inner casing 42 and the elements containedtherein, it will be seen that the resonator 50 has preferably associatedtherewith a circumferentially positioned release vent 61.

The vibrating member 50, adapted to actuate by air auditoryoscillations, may be formed in various shapes, as shown in the drawingsand as described herein. In the embodiment shown in FIGURE 3, thevibrating elementthereof consists of a tapered or conically shapedhelical spring member 51. This spring may be formed of any desiredmaterial having the requisite tensile strength and mass in relation tothe mass of the diaphragm 53, and has its axis substantiallyperpendicular to the plane of said diaphragm.

Spring member 51 is preferably formed of a flexible, planar, metallicmaterial, but may, of course, be formed of other materials, such asthose generically designated as plastics. In this preferred form of theinvention the material of the member 51, and the formatory heattreatment thereof, are so selected that the spring member has aninherent, or natural, basic vibratory frequency which is containedwithin the above-descibed spectrum of human speech. This predeterminednatural resonant frequency of the vibrating member preferably occurs atthe peak of normal human speech. Thus, for example, the spring has apreselected resonant frequency in the range of from about 300 to about400 cycles.

It will be understood that the vibrating member, or spring element 51and chamber 60 respond to reverberation of the diaphragm to acousticallyabsorb undesirable sound noises and reradiate the desirable soundpassing through the acoustic capsule 40, thus, in effect, acting as anacoustic wave guide attenuator, since the undesirable noise frequenciesare selectively attenuated.

As the coupled reverberation of the chamber 60, the diaphragm 53 and thespring member 51 intensifies, acoustic scattering takes place within theouter chamber, or air space, of the capsule 40 designated as 70; theenergy received from auditory atmospheric vibrations is thus sotransmitted through the spring as to create an acoustic delay line.

The spring 51, being fundamentally resonant to the basic frequencies ofhuman voice energy will, of course, transmit additional desired secondand third harmonics and the like into the sonic vibration of theabove-described members, these vibrations being in addition to thedesired fundamental frequencies to which the spring is attuned.

Reference is now made in more detail to the diaphragm 53 which acts, ineffect, as a tympanum. Since this diaphragm constitutes a flexible wallof the acoustic vibratory chamber, or resonator 60, contained within thecapsule 40, it will resonantly transmit the fundamental and harmonicportions of speech energy into pneumatic pulsations through a vibratorypumping action.

This transduced energy, primarily consisting of low intensitycomponents, causes reinforcement of the received human speech syllableswhich are, in effect, auditorily and by ear pulsation, pumped throughthe above-described release vent 61 into that interior portion 15 of theear canal 11 which is interior of the capsule 40, throughcircumferential area 66. These vibrations then in turn serve tostimulate the eardrum and its associated auditory system.

There has been shown and described a simple acoustic delay line,including means for both amplifying, discriminating and time delayreinforcing the desirable components of the sound spectrum whichcorrespond to intelligible human speech.

It is to be further understood that the storage and dissipationefliciency of the device of the invention are determined by both thegeometry and mass of the resonator 60 and by the configuration andfundamental resonant frequency of the vibrator 50, and by the mass andsensitivity of the diaphragm 53.

Thus, the tone frequency noise filter of the invention is responsive ina major degree to speech energy and is responsive in a substantiallylesser degree to background noise energy.

The preferred configuration described above selectively directs, at oneor more preselected deflection angles, the received sound energy, SO asto direct this energy into contact with the diaphragm and vibrator.While only one configuration of this inlet system has been shown, itwill be understood that one or more similar apertures, of any desiredshape or direction, may be utilized, so long as they coact toselectively place sound energy on a particular part or parts of thevibrating member for frequency selective attenuation of undesired sound.

In a preferred embodiment of the invention the resonating diaphragm isformed of a simple planar, flexible, metallic material. The choice ofthis material is determined by factors such as cost, acoustic responsecharacteristics thereof, and the like.

Referring again to FIGURE 3, it is seen that the inner casing 42, whichcontains the vibrator 50, is preferably generally bullet-shaped in formso far as the casing end 42' is concerned, and has at the other end 46thereof a generally uniplanar wall surface 43. There will be furthernoted that at this apex or end 42 of the inner casing 42 there is formedan additional aperture 80, comprising a transmission passage. Fittedwithin this aperture is a further sound transmitting member 82 having agenerally axial, annular projection 84 which is substantially conformedto the aperture 80, by screw fit or the like. At the end of this member82 there is positioned an annulus having a larger diameter than that ofthe said aperture 80.

Positioned interiorly of, and extending through this member, are one ormore bores or passages 88, 88. Incoming energy of undesirable frequencyis, with proper selection of the size of the bore or bores, leakedthrough the capsule and member 82. However, the desired speechfrequencies are not predominantly within that portion of the spectrumwhich passes through the bore or bores 88. Thus, in effect, this portionof the apparatus acts to selectively attenuate undesired frequencies byscattering the energy contained therefrom in a non-vibratory fashion.These undesirable frequencies, having passed by air coupling through thebore or bores 88 are reduced to minimal desired intensity, so that asmall portion of the initial undesirable auditory energy is transmittedor acoustically coupled to the inner car 16.

This selective coupling to the human auditory system of a small portionof background noises is desirable in order to produce nerve sensedsignals which appear to the nerves and brain as natural. In other words,complete filtration of the background noises is not desirable, since thesound which is perceived by the human brain is then unnatural, notcorresponding to normal environments, in which at least some level ofbackground noise is generally present.

There has been previously dscribed a single form of v brating member,designated generally as 51, whose quallties have been described indetail hereinabove.

I In FIGURES 4, 5 and 6 there are also shown alternative embodiments ofequivalent structures of the vibratmg member 51 per se. It will beunderstood that in each of these figures there is shown in broken linefashion a cross-sectional portion of the vibrating members 51 which arecoupled to the vibrating membrane or diaphragm 53; in each of thesealternative embodiments, it is to be further understood that theremaining elements of the invention are equivalent to those which havepreviously been described.

Considering now FIGURE 4, the numeral 53 designates the diaphragm towhich there is mechanically coupled, in the manner previously described,and for the purposes previously described, one or more spring members 90having individual coils, generally axially aligned, and designatedgenerally as 91. These coils '91 have coupled thereto in vibratoryrelation energy transmitting members 92 which are supported by diaphragmmember 53.

In FIGURE 5 there is shown a somewhat similar embodiment. In thisembodiment vibratory spring members 100, have at their junction a middlemember 102 and at their ends have members 101 and 101. Members 101, 101and 102 are mechanically, vibratorily coupled to diaphragm 53.

In FIGURE 6 it will be noted that a basic vibrator 200 has coupledthereto other spring elements 200, 200, and similar vibratorytransmitting members 201, 201.

By proper predetermined selection, as explained hereinabove, of theconfiguration and materials of the resonator, acoustical chamber,vibrator, end bores, the noise filter may be selectively attuned fordesired sound transmission. To accomplish this, adjusting means shownschematically at 300 may be utilized to alter the resonant frequency ofthe vibrator 50 or the sound transmitting member 82. Means 300constitute an adjustable short circuiting means coupled to spring 51.Other means may be used to adjustably bias or to longitudinally positionelement 82.

It is to be understood that in all of the above embodiments the vibratorincludes elements which have a natural resonant frequency in relation tothe input of auditory air stimulation, this frequency being determinedby the choice of materials, as described above, and being furtherdetermined by, in the case of a plurality of coils or vibratory members,their interrelation.

What is claimed is:

1. A tone frequency noise filter comprising, in combinati-on a capsulemember adapted to be inserted within the human auditory canal,

a diaphragm member positioned within said capsule,

a vibratory member, having frequency discriminatory properties, andadapted to be actuated by air oscillation and operatively coupled tosaid diaphragm member, and

means to direct auditory air oscillations to said capsule, whereby theoutput of said tone frequency noise filter is responsive in a majordegree to speech energy and is responsive in a lesser degree tobackground noise energy.

2. The tone frequency noise filter of claim 1 wherein the said vibratorymember has a preselected natural resonant frequency.

3. The tone frequency noise filter of claim 2 wherein the said frequencyis within the range of from about 300 to about 400 cycles per second.

4. The tone frequency noise filter of claim 2 wherein the said frequencyis within the range of from about 40 to about 3900 cycles per second.

5. The tone frequency noise filter of claim 1 wherein the vibratorymember consists of a helical spring.

6. The tone frequency noise filter of claim 5 wherein said helicalspring is of conical shape, and has an axis which is positionedsubstantially perpendicular to said diphragm member.

7. The tone frequency noise filter of claim 1 wherein the vibratorymember consists of a plurality of springs of substantial-1y helical formand wherein at least one end of each of said plurality of springs isoperatively connected to said diaphragm member.

8. The tone frequency noise filter of claim 1 wherein said capsule hasan end member and wherein said end member has positioned therein a soundtransmitting member having at least one bore having a preselected sizeand which bore is adapted to be directed towards the interior of a humanauditory system.

9. The tone frequency noise filter of claim 1 wherein said capsulefurther includes an outer casing, and an inner casing, and wherein saidinner casing has formed therein a vibratable acoustical chamber.

10. The tone frequency noise filter of claim 9 wherein said inner casingincludes a generally planar surface at one end portion thereof and agenerally bullet-shaped other end portion.

11. The tone frequency noise filter of claim 10 wherein the saidbullet-shaped end portion has bore means positioned therein, which boremeans is capable of transmission of auditory oscillation.

12. The tone frequency noise filter of claim 1 wherein said capsuleincludes means to selectively direct auditory energy to said diaphragmand to said vibratory member.

13. The tone frequency noise filter of claim 12 wherein said directingmeans comprises a transmission passage positioned in an end wall ofsaid' capsule, said directing means being adapted to provide a source ofauditory oscillations derived from said vibratory member and saiddiaphragm.

14. The tone frequency noise filter of claim 1 wherein said diaphragmmember consists of a flexible, metallic planar member.

15. The tone frequency noise filter of claim 1 wherein said capsule hascontained therein an acoustical vibratory chamber.

16. The tone frequency noise filter of claim 15 wherein said chamber hasa circumferentially positioned vent therein.

17. The tone frequency noise filter of claim 9 wherein an air space isformed between said inner and outer casing.

18. The tone frequency noise filter of claim 1 wherein said capsule hasan end surface and wherein said end surface has positioned thereon amanually graspable projection.

19. The tone frequency noise filter of claim 11 wherein there ispositioned within said bore means a member having a generally annularand axial portion fitted within said bore, a passage through said axialportion and an end portion whose diameter is greater than that of saidbore.

20. The tone frequency noise filter of claim 2 wherein the structureincludes means for selecting said preselected natural resonantfrequency.

References Cited UNITED STATES PATENTS 1,824,427 9/1931 Fensky 181-231,908,850 5/1933 Kinsley et al. 18'1-23 3,394,698 7/1968 Calkins 128--1FOREIGN PATENTS 428,733 5/ 1935 Great Britain.

STEPHEN I. TOMSKY, Primary Examiner.

US. Cl. X.R.

